The invention will be described by way of example with reference to engines such as two and four stroke engines operating on petrol or equivalent or substitute fuels. It should be appreciated that this is by way of example only and other engine types may also be configured or constructed to incorporate the improved construction of the present invention.
With present engines of this general type, one or more pistons are arranged to reciprocate within the cylinders in which combustion takes place. The pistons undertake reciprocal movement between a bottom dead center position and a top dead center position to cause compression of a fuel/air mixture until ignition occurs and progress through an exhaust stroke of the cycle. Ignition always occurs at one location within a combustion chamber defined by the cylinder, the engine head and one end of the piston and thus for combustion to occur the piston must always return towards top dead center. Thus, the piston moves along its reciprocating path and not all of this movement can be utilized in converting linear motion into rotary motion.
Engines have been proposed where pistons move along an arcuate rather than a linear path. U.S. Pat. Nos. 4,870,869 and 4,038,948 show engines where the piston moves along an arcuate path defined by an arcuate cylinder within a cylinder block. The driving force to be transmitted in such an engine is transmitted with higher efficiency than is the case with engines having linearly reciprocating pistons. However, the disadvantage previously referred to, namely that not all of the reciprocating motion is converted into rotary motion, still exists.
U.S. Pat. No. 3,910,239 is an attempt at minimizing this deficiency. This specification discloses an engine having a single cylinder curved about a center, intake and exhaust ports at opposite ends of the cylinder and a pair of opposed positions moveable in the cylinder towards and away from each other in compression and power strokes. The pistons cause rotation of separate crankshafts rotating in opposite directions and a more balanced engine results.